MIAMI - Red tide has killed 174 manatees along the southwest Florida coast.

With no sign of when the deadly algae bloom might abate, the preliminary death toll for the endangered animals is likely to continue rising, state and federal wildlife managers said Monday. The number of deaths already has topped the 151 killed by red tide in 1996.

"It's really hard to make any kind of prediction on it," said Kevin Baxter, a spokesman for the Florida Fish and Wildlife Conservation Commission. "Each outbreak is a little different."

This red tide covers roughly 70 miles from Sarasota on the Gulf Coast south to Pine Island Sound, where most of the deaths have been recorded in warm waters where the sea cows congregate in winter. Sampling has found the algae, which also has triggered sporadic fish kills, as far south as Collier County at times.

Baxter said most commission scientists believe the manatees are dying after eating sea grass, a staple of their diet, that the algae had settled on. Once afflicted, they lose coordination and the ability to swim upright or lift their heads out of the water to breathe.

If reached early, stricken manatees can be saved, Baxter said. A dozen have been rescued so far, taken to area zoos where workers hold their heads above water until the effects fade.

The manatee has more than doubled its population over the last few decades, with estimates of more than 4,000 now in state waters. The U.S. Fish and Wildlife Service, petitioned by boating and development interests, has begun working on a proposed rule to reclassify the manatee from endangered to threatened, which could slow or halt the expansion of slow-speed and idle zones in state waters. Despite the larger population, environmentalists argue that the manatee remains highly vulnerable to boat strikes, cold weather and red tides.

Development also has destroyed much of its natural habitat, and the phase-out of coastal power plants could reduce warm-water havens that protect them during cold snaps.